The chemical cue tetrabromopyrrole from a biofilm bacterium induces settlement of multiple Caribbean corals

Abstract

Microbial biofilms induce larval settlement for some invertebrates, including corals; however, the chemical cues involved have rarely been identified. Here, we demonstrate the role of microbial biofilms in inducing larval settlement with the Caribbean coral Porites astreoides and report the first instance of a chemical cue isolated from a marine biofilm bacterium that induces complete settlement (attachment and metamorphosis) of Caribbean coral larvae. Larvae settled in response to natural biofilms, and the response was eliminated when biofilms were treated with antibiotics. A similar settlement response was elicited by monospecific biofilms of a single bacterial strain, Pseudoalteromonas sp. PS5, isolated from the surface biofilm of a crustose coralline alga. The activity of Pseudoalteromonas sp. PS5 was attributed to the production of a single compound, tetrabromopyrrole (TBP), which has been shown previously to induce metamorphosis without attachment in Pacific acroporid corals. In addition to inducing settlement of brooded larvae (P. astreoides), TBP also induced larval settlement for two broadcastspawning species, Orbicella (formerly Montastraea) franksi and Acropora palmata, indicating that this compound may have widespread importance among Caribbean coral species.

Crustose coralline algal species host distinct bacterial assemblages on their surfaces

“…Both of the CCA species that have been shown to be avoided by coral larvae, P. solubile and P. pachydermum, have high abundances of bacteria that are closely related to known coral pathogens (Vibrios and Rhodobacteraceae) or cyanobacteria that are known to produce allelopathic compounds (Oscillatoriales). Coral larvae respond to a variety of physical and chemical cues (Gleason and Hofmann, 2011) during the settlement process including the presence of bacterial biofilms and specific bacterial strains within biofilms (Negri et al, 2001;Tran and Hadfield, 2011;Sneed et al, 2014). Gleason and Hofmann (2011) proposed a 'hierarchy of action' in which coral larvae hone in on a settlement location through a series of cues that function at increasingly smaller spatial scales.…”

“…What is known to date about the role of bacteria in the induction of coral larval settlement has focused on the role of individual bacterial strains. Several strains have been shown to induce settlement, suggesting that the presence of specific inductive species is more important than the overall diversity of the bacterial community (Negri et al, 2001;Tebben et al, 2011;Tran and Hadfield, 2011;Sneed et al, 2014). However, little work has been carried out to examine the importance of multispecies conglomerations of bacteria on larval settlement preferences.…”

“…On the basis of these preferences, it is clear that some coral larvae are capable of recognizing and discriminating among CCA species, however, the mechanism by which they are able to differentiate among CCA is unknown. There is growing evidence that bacteria associated with potential settlement substrata induce settlement activity in many invertebrates including corals (Webster et al, 2004;reviewed in Hadfield, 2011), and that in some cases, they respond to specific bacterial strains within the bacterial community (Negri et al, 2001;Tebben et al, 2011;Tran and Hadfield, 2011;Sneed et al, 2014). It is therefore likely that larvae may use bacteria to recognize appropriate settlement substrata.…”

Reclutamiento del coral Acropora palmata sobre sustratos de dos materiales

“…Segundo, el número de reclutas registrados en este estudio se subestimó, ya que no se cuantificaron los reclutas que también se fijaron sobre la rejiluz y las paredes (incluyendo la malla) y el fondo de las cajas de reclutamiento, ni otros pólipos primarios calcificados que se mantuvieron flotando. Se ha sugerido que estos pólipos no se fijan debido, entre otras posibles causas, a cualidades insuficientemente propias de los sustratos (Harrison & Wallace 1990, Sneed et al 2015. Las causas (no mutuamente excluyentes) de la discrepancia entre muchas larvas y pocos reclutas indican que el protocolo seguido en acuario para el maricultivo de A. palmata requiere de ajustes que contribuyan al incremento en la obtención de reclutas sobre los sustratos experimentales.…”

Bacterial Biofilm Communities and Coral Larvae Settlement at Different Levels of Anthropogenic Impact in the Spermonde Archipelago, Indonesia

“…Settlement of invertebrate larvae is assumed to be triggered by bacteria in biofilms (Huggett et al, 2006;Sneed et al, 2014). Reports of interactions between larvae and bacteria exist for many marine invertebrates such as sponges, echinoderms, bryozoans, ascidians, crustaceans, and corals (Hadfield, 2011).…”